1. Field of the Invention
The present invention is directed generally to systems for electrofusing thermoplastic, and, more particularly, to a cordless apparatus for electrofusing thermoplastic.
2. Description of the Background
Because of its low cost, durability, and relative ease of installation, polyethylene thermoplastic pipe has become a commonly accepted mode of distribution of natural gas and water in both residential and commercial applications. Unions between two pieces of thermoplastic pipe and branch connections between a main pipe and a branch pipe are commonly made through the use of electrofused unions.
Electrofusing is especially useful in forming branch connections or for tapping into main pipelines. A thermoplastic tapping tee can be placed on the main pipe and electrofused to the main pipe to create a leaktight weld between the main pipe and the tapping tee. The main pipe is then perforated by a perforation device located in the tapping tee. A branch pipe is connected to the tapping tee and the desired tapped-in connection is thus established.
A typical tapping tee 1 and apparatus 2 for electrofusing thermoplastic pipe from the relevant art are illustrated in FIG. 5. The tapping tee 1 in FIG. 5 contains electrically resistive elements which are embedded in its thermoplastic. When an electric current is supplied by the electrofusion apparatus 2 through a pair of leads 3 to the resistive elements, the fusible portions of the tee 1 and portions of a main pipe 4 melt and create leaktight welds between the tee 1 and the main pipe 4. The connectors on the tee 1 for accepting the leads 3 contain fusion wells. When the resistive elements generate heat, molten plastic from the tee 1 and the main pipe 4 is forced into the fusion wells. Pressure from the molten plastic causes microswitches in the leads to signal the electrofusion apparatus 2 to cease supplying electrical current to the tee 1 to indicate the electrofusion is complete. Such switches are illustrated in U.S. Pat. No. 4,684,417 to Grandclement, which is incorporated herein by reference.
The electrofusion apparatus 2 shown in FIG. 5 uses an alternating current source 5 to generate the current required to form the electrofused joint. The apparatus 2 shown in FIG. 5 has the disadvantage that it must be connected to the alternating current source 5, which may not be readily available to a contractor or a pipe installer in a remote location. Use in a remote location would thus require the use of an alternating current generating source, such as a gasoline powered or other powered generator. Such generators are expensive, difficult to transport, difficult to service, a potential safety hazard, unreliable, and potentially dangerous. Also, because the electrofusion apparatus 2 of FIG. 5 accepts alternating current, it must "clip" the alternating current supplied to it to make a root mean square (RMS) voltage or it must convert the alternating current to direct current. Thus, the apparatus 2 is bulky, expensive and may be cumbersome to handle and use in field applications.